In the related art, a semiconductor thin film such as polycrystalline silicon (poly-Si) is widely used for a thin film transistor (TFT) or a solar cell. As a method for inexpensively forming the semiconductor thin film, the semiconductor thin film is crystallized by emitting laser beams to an amorphous silicon film. A laser process can also be applied to activation of impure atoms introduced into a semiconductor substrate by means of ion implantation or plasma doping. However, this laser annealing technique has a disadvantage in that an attainable temperature greatly varies or a seam appears depending on whether a heating object absorbs light a lot or a little, and additionally requires very expensive equipment.
Therefore, a technique has been studied in which heating can be performed by generating elongated thermal plasma and by performing scanning in only one direction without depending on light absorption by the heating object, and in which thermal processing is inexpensively and seamlessly performed (for example, refer to Japanese Patent Unexamined Publication Nos. 2013-120633, 2013-120684, and 2013-120685, and T Okumura and H. Kawaura, Jpn. J. Appl. Phys. 52 (2013) 05EE01).